DISTINCTION BETWEEN COMPOUNDS AND MIXTURES
The following example of iron, sulphur and iron sulphide will make us understand the difference between mixtures and compounds.
Properties of Iron and Sulphur
The following experiment shows the difference in properties between the elements iron and sulphur.
Preparation of a Mixture of Iron and Sulphur
Take about 7g of freshly powdered iron, and a little more than 4 g of sulphur. Mix them well. However well it may be mixed, the iron and sulphur particles can be seen separately.
Also the above said properties of both iron and sulphur will still be exhibited by this mixture.
Preparation of Iron Sulphide
Take this mixture of iron and sulphur in a hard glass test tube. Heat over spirit lamp or burner.
The sulphur starts melting. Then the mixture catches fire. Stop heating. The flame spreads throughout the mixture, evolving heat.
When it dies out, heat the test tube very strongly, so that any extra unreacted sulphur gets burnt out.
Dip the red-hot test tube in cold water. The test tube breaks. Collect the iron sulphide formed, and powder it.
Compare the properties of the mixture of iron and sulphur with that of the iron sulphide formed.
Comparison of properties of a mixture of iron and sulphur with iron sulphide is shown below.
Comparison of properties of a mixture of iron and sulphur with iron sulphide
Solutes and solvents
When a salt is mixed with water and the mixture stirred, a solution is produced.
The salt is the solute, water is the solvent and the resulting mixture is called a solution.
Solute – A substance that will dissolve in a liquid e.g. salt.
Solvent – A liquid into which a substance dissolves e.g. water.
Solution – Is a uniform mixture of solute and solvent.
Miscible and Immiscible substances
- Miscible: These are substances capable of being mixed. They are soluble in each other. Water and alcohol are miscible as they dissolve to make a solution.
- Immiscible: These are substances that cannot be mixed. They do not dissolve in each other. Oil and water are immiscible. They separate into two layers, e.g. paraffin and water.
Homogeneous and Heterogeneous mixtures
Water and alcohol are completely miscible.
They make a homogenous solution. In other types of mixture, the state remains separate.
This is known as an heterogeneous mixture. There are a good number of substances that make hetegeneous mixtures.